Computational methods for signal processing provide foundation technologies for many different types of systems and services, including systems and services related to recording, transmission, and rendering of signals that encode images and graphics, including photographic images, video signals, and other such signals. Over the years, many different types of image-enhancement functionalities have been devised and implemented, including computational routines and/or logic circuits that implement sharpening, contrast enhancement, denoising, and other image-enhancement functionalities. Contrast enhancement is a general term to describe a number of different types of enhancements, including global enhancements such as brightening, darkening, histogram stretching or equalization, gamma correction, and others, as well as local enhancements, including shadow lighting, adaptive lighting, highlight enhancement, and others. Many contrast enhancement algorithm are successful in producing certain of the above enhancements, but are not successful in achieving other types of enhancements. In particular, significant research and development efforts have been directed to developing techniques for enhancing image signals to increase appreciation, by viewers, of two-dimensional images rendered from the image signals. Unfortunately, contrast enhancement techniques often result in uneven effects, and may lead to introduction of perceptible anomalies and artifacts. For these reasons, designers, developers, vendors, and users of image-enhancement software, image-enhancement-related logic circuits, image-enhancement-related systems and devices, and a large number of different types of devices that include image-enhancement functionality have all recognized a need to continue to devise and develop improved computational methods for well-known and new contrast enhancements as well as systems that provide more natural, computationally efficient contrast enhancement of two-dimensional images and other signals, including signals that encode video frames, graphics, and other visually displayed information.